cylinder 7 misfire help
cylinder 7 misfire help I have a built 408 tsp motor ms4 cam 247 heads 42lb injectors. The motor has roughly 10000 trouble free miles on it, and yes I daily drive it. The car had run great until last week It started running a little shitty. Hard to idle power cutting in and out just not right. So far I replaced the plugs and wires, i also swapped the coil and also injector from another cylinder just to rule them out. What next?
On The Tree
Joined: Aug 2012
Posts: 190
Likes: 0
You should start it cold, and see if the #7 primary tube gets hot within a few seconds. If it doesn't that cylinder isn't firing, if you have already swapped coils/wires/plugs and it stayed at that cylinder, it's either the wiring to that coil or a bent valve. A compression test will let you know if it's mechanical or electrical, just compare it to the #5 cylinder.
On The Tree
Joined: Aug 2012
Posts: 190
Likes: 0
If it's a pushrod the compression will be good, since it's not opening the valve as much. You can check the pr by rolling it on glass. The valve "head" only has to be bent a tiny amount to not seal, and can't be detected with the head on, autozone/oreileys has a compression tester to rent. Just disconnect the two coil harness plugs and pull out the fuel pump fuse. Crank the engine a few seconds until the comp gauge stops moving and see where it stops. I'm only saying all this because I went through the same situation, black plug, vibration at idle, loss of power, no codes but it smelled rich. An engine needs around 90psi to fire, if it can't build compression it won't fire and you end up with a black plug.
Trending Topics
The right scan tool can show active misfire(s) for a particular cylinder. I have seen an ECM with bad injector driver have/ cause intermittent misfire. It may not be mechanical.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
Five Reasons the Camaro Was the Most Pivotal Player in the Pony Car Wars 2.0
Brett Foote I really hope its not, this motor cost me nearly 10k from Texas speed and I cant see it having 10k miles on it yet. I just dont get where any damage would have come from out of nowhere. Ill dp a compression test tomorrow and see what its lookin like. Say a prayer everyone
I also left something out that may be part of it. My starters been weak for a while and last weak while trying to get it to turn over while it was struggling to turn over it started to pour out smoke under or near the alternator. I couldn't pin point the location but while changing the starter I noticed the main engine ground from the battery wasn't hooked up for some reason. So all I've has for a ground was the battery to chassis and one small ground strap from the block to chassis. After I fixed the ground I noticed the biggest difference in starting. Im not taking blame for the ground im assuming the shop I paid to install the oil pan and k member a few months back forgot to hook it back up. Figures the one and only time I pay someone to do a job they forget something, I couldn't do it myself bec I was fresh out of the hospital with no use of my upper body lol
When I popped the valve cover off everything looked fine all the rockers were tight and the pushrods seemed straight and tight so correct me if im wrong but would I have a noticeable amount of play in the pushrod if a lifter went?
It depends on where the cam lobe is.
I completely forgot about that wow. Ill check it again tomorrow. But tonight I did a compression test on all the cylinders and they were all about 190 so thats definitly a big relief. But the new plug I put in cylinder 7 was black again
Does it smell like fuel?
It could be an oiling issue that's taking that cylinder out too. Look though the valve springs and see if you can see if the valve seal has walked up off the guide boss.
I would turn the engine over by hand with the valve cover off and see if both rocker arms are moving about the same amount.
Also when there is full lift on one valve check the other to check to see if there is any slack. Keep in mind after you spin the motor over a few times by hand the lifter is going to bleed off some so take that into consideration.
If that looks good I would pull both pushrods out and make sure their straight and while they are out do a leak down test.
That way you can pretty much eliminate anything mechanical or find out that's the problem.
It could be an oiling issue that's taking that cylinder out too. Look though the valve springs and see if you can see if the valve seal has walked up off the guide boss.
I would turn the engine over by hand with the valve cover off and see if both rocker arms are moving about the same amount.
Also when there is full lift on one valve check the other to check to see if there is any slack. Keep in mind after you spin the motor over a few times by hand the lifter is going to bleed off some so take that into consideration.
If that looks good I would pull both pushrods out and make sure their straight and while they are out do a leak down test.
That way you can pretty much eliminate anything mechanical or find out that's the problem.
Both rockers are moving pretty close to the same amount. I cant really tell if the seal moved as I have dual valve springs. I can just barely see the top of the seal and theirs no noticeable smoke coming out of the exhaust so i don't think thats it. I feel like the bad ground burn out the computer
So once I stop cranking to see the rockers mover I noticed all of the rockers go to the highest point right away but one of the #7 rockers is keeping the valve slowly bleeding back closed within a few second. Im trying to figure out how to post a video now so you can all see what I mean and if this is normal or not
OP: bring #7 to top dead center and see if you can push the pushrod end of the intake & exh rocker down at all. There is usually an audible ticking noise accompanying lifter failures...any noise on yours?